Process and device for making secure the processing of safety signals, on lifting apparatus

ABSTRACT

The invention makes secure the processing of a signal (Se) delivered by a sensor ( 2 ) of resistive analog type, in a safety device, the signal (Se) being converted into a digital signal (n) in an analog/digital converter ( 4 ) of resolution (R). A digital signal (n 1 ) is acquired and stored, then the supply voltages (Va, Vb) of the sensor ( 2 ) are inverted (at  8 ) and a new digital signal (n 2 ) is acquired. The two signals (n 1 , n 2 ) are summed, and their sum (S) is compared with the resolution (R) of the converter ( 4 ). Depending on whether the sum (S) is or is not equal to the resolution (R), the control (Cm) of an actuator ( 6 ), corresponding to a pre-set (Sc), is enabled or otherwise.  
     Application to tower crane safety devices.

[0001] The present invention relates, in a general manner, tomonitoring/control devices for lifting apparatus, and more particularlyto safety devices such as load limiters, torque limiters, motion(lifting, rotation, distribution, translation) limiters or speedlimiters, provided on lifting apparatus such as tower cranes.

[0002] More particularly, the invention pertains to the making secure ofthe processing of the signal of the sensors of these safety devices,usually embodied in the form of sensors of resistive analog type,supplied electrically with DC current.

[0003] Among monitoring systems of safety devices of lifting apparatus,one generally encounters systems employing so-called “passive” analogsensors, that is to say ones which have to be supplied with power inorder to operate, for example potentiometers, gauges or probes, thesesensors being chosen on account of their low cost, their proventechnology and their serviceability.

[0004] The use of monitoring systems of this kind, on lifting apparatus,requires that the acquisition pathway be made secure, this pathwayconditioning and transmitting the analog signal delivered by a passivesensor such as this.

[0005] To make this acquisition pathway secure on lifting apparatus, theonly known solution currently used is the redundancy of the circuitswith comparison of the values acquired. Such a system is applied inparticular on tower cranes constructed by the applicant company POTAIN.

[0006] The major drawbacks of this existing solution are its cost, itscomplexity of installation and its restricted availability since itleads to a doubling-up of the risks of malfunctioning.

[0007] The present invention aims to avoid these drawbacks, by providinga solution which, for identical security, is appreciably simpler andmore economical, and reduces the risks of malfunctioning of the system.

[0008] Accordingly, the subject of the invention is essentially aprocess for making secure the processing of safety signals, moreparticularly of a signal delivered by a sensor of resistive analog type,supplied electrically with DC current, in a safety device on a liftingapparatus, the analog signal delivered by the sensor being convertedinto a digital signal in an analog/digital converter of givenresolution, the process being characterized in that:

[0009] at a first instant, a digital signal corresponding to the analogsignal delivered by the sensor is acquired and stored,

[0010] then the supply voltages of the sensor are inverted,

[0011] after this inversion, at a later instant, a new digital signalcorresponding to the analog signal delivered by the sensor is acquired,

[0012] the two digital signals acquired are summed,

[0013] the sum of these two digital signals is compared with theresolution of the analog/digital converter, and

[0014] if this sum is equal or approximately equal to the resolution ofthe converter, a control signal for operating an actuator of the liftingapparatus, corresponding to a control pre-set, is enabled, or

[0015] if said sum is significantly different from the resolution of theconverter, the control signal is not enabled.

[0016] Thus, the principle of the invention relies on the possibility ofchecking the operation of the pathway for acquiring the signal of aresistive analog sensor, simply by inverting the supply voltages of thissensor.

[0017] In the event of correct operation, the two digital signals,acquired respectively before and after this inversion, are“complementary”, that is to say their sum is constant, and equal to theresolution of the analog/digital converter. Conversely, in the event ofmalfunctioning, the sum of the two relevant digital values is no longerequal to this resolution, thus allowing this malfunctioning to bereadily detected.

[0018] According to a preferred mode of implementation of the processwhich is the subject of the invention, the analog signal, delivered bythe sensor, is filtered and matched, so as to yield a digitizable analogsignal which is the signal to be converted, before and after inversionof the supply voltages of the sensor.

[0019] Advantageously, in the case where the calculated sum of the twodigital signals is significantly different from the resolution of theanalog/digital converter, a signaling is emitted to indicate the stateof malfunctioning.

[0020] The subject of the invention is also a device for theimplementation of the process defined above.

[0021] This device is defined, essentially, as a device for makingsecure the processing of safety signals, more particularly of the signaldelivered by a sensor of resistive analog type, supplied electricallywith DC current, in a safety device on a lifting apparatus, the sensorbeing linked to an analog/digital converter of given resolution, whichconverts the analog signal delivered by the sensor into a digital signaltransmitted to an arithmetic and logic processing unit which alsoreceives a control pre-set, and which is able to deliver a controlenable signal for operating a motion actuator for moving the liftingapparatus, the device being characterized in that it comprises, incombination:

[0022] control means for inverting the supply voltages of the sensor,

[0023] means for acquiring the digital signals corresponding to analogsignals delivered by the sensor, respectively before and after inversionof its supply voltages,

[0024] means of summing the two digital signals acquired, and ofcomparing the sum of these two signals with the resolution of theanalog/digital converter, and

[0025] means of enabling/disabling the control of the actuator,corresponding to the pre-set, according to the result of the comparisonof the aforesaid sum with the resolution of the converter.

[0026] The sensor being in particular a potentiometer, the means ofcontrol of inversion carry out the inversion of the supply voltagespresent at the terminals of the potentiometer.

[0027] Preferably, an analog conditioning circuit, intended forfiltering and matching the analog signal delivered by the sensor, suchas a potentiometer, is interposed between this sensor and theanalog/digital converter.

[0028] In an advantageous embodiment of the device of the invention, themeans of acquiring the two digital signals, of summing these signals, ofcomparing the sum of these signals with the resolution of theanalog/digital converter, and of enabling/disabling the controlaccording to the result of the comparison, are incorporated into thearithmetic and logic processing unit, the latter possessing an outputlinked to the means of control of inversion of the supply voltages ofthe sensor, which means are embodied in the form of an inversioncircuit.

[0029] Advantageously, the arithmetic and logic processing unit,incorporating (as indicated above) the means of acquiring the twodigital signals, of summing these signals and of comparing their sumwith the resolution of the converter, is embodied in the form of amicroprocessor.

[0030] By virtue of the process and of the device which are the subjectof the invention, it becomes possible to implement a single sensor,instead of two sensors (for redundancy of the circuits, according to theprior technique), whilst still obtaining identical security, or evenimproved security. The invention also leads to a simplification of thewiring of the relevant lifting apparatus, since it requires the wiringof just one sensor, instead of two, hence a saving. Moreover, theinvention diminishes the causes and decreases the risks ofmalfunctioning, since it implements a single security circuit, insteadof two circuits. Finally, the system proposed by this invention isalmost 100% reliable, and self-monitored: if the security circuit isitself defective, it does not instruct the inversion of the supplyvoltage of the sensor, so that the complementarity of the two digitalsignals is no longer ensured, and hence the system goes faulty.

[0031] The invention will in any case be better understood with the aidof the description which follows, with reference to the appendeddiagrammatic drawing representing, by way of example, an embodiment ofthis device for making secure the processing of safety signals, onlifting apparatus:

[0032]FIG. 1 represents the device which is the subject of theinvention, in the form of a functional diagram.

[0033]FIG. 2 is a flowchart which illustrates the operation of thisdevice.

[0034]FIG. 1 represents a certain number of elements of amonitoring/control system, known per se, to which the invention applies.

[0035] Thus, the system comprises a sensor 2 of resistive analog type,for example (as illustrated in the figure) a potentiometer, mountedsuitably on a lifting apparatus. The sensor 2 is supplied electricallyvia a DC voltage (Vb−Va), Va and Vb designating the electrical voltagespresent respectively at the two extreme terminals of the potentiometer.The sensor 2 consisting of this potentiometer delivers an analog signalSe, dependent on the position of the slider of this potentiometer.

[0036] The system also comprises an analog conditioning circuit 3,intended for filtering the glitches and for matching the signal of thesensor 2. At its input this circuit 3 receives the signal Se, anddelivers an analog signal Ss at its output.

[0037] The system further comprises an analog/digital converter 4, ofresolution R, this resolution being for example 12 bits so that saidconverter can deliver digital values from 0 to 4095. At its input thisanalog/digital converter 4 receives the matched analog signal Ss, and atits output it delivers a digital signal, stated otherwise an integernumber n, corresponding to the input signal Ss, hence to the signal Seof the sensor 2.

[0038] Finally, the system comprises in a known manner an arithmetic andlogic processing unit 5, which can be embodied in the form of amicroprocessor. The unit 5 receives the digital signal n delivered bythe converter 4. It also receives a control pre-set Sc delivered by theoperator of the lifting apparatus. This unit 5 delivers or otherwise acontrol signal Cm, so as to enable or otherwise the control of anactuator 6 of the relevant motion of the lifting apparatus, the actuator6 generally being a motor, electric or hydraulic.

[0039] The security device which is the subject of the invention alsocomprises the arithmetic and logic processing unit 5, in particular inthe form of a microprocessor, and a specific output 7 of this unit 5.This device further comprises a circuit 8 for inverting the supplyvoltages Va and Vb of the sensor 2, the output 7 of the unit 5 beinglinked to the input of the circuit 8.

[0040] The inversion circuit 8 possesses two outputs, on which arerespectively present the two voltages Va and Vb, these two outputs beingrespectively connected to the two terminals of the potentiometerconstituting the sensor 2.

[0041] The arithmetic and logic processing unit 5 is designed todeliver, on its output 7, a command Si for inverting the supply voltagesof the sensor 2, according to an algorithm. This command Si istransmitted to the inversion circuit 8, which then orders the inversionof the supply voltages of the sensor 2. For example, before theinversion, the voltages at the outputs of the circuit 8 are: Va=−5 voltsand Vb=+5 volts, whereas after inversion, these two voltages become,respectively: Va=+5 volts and Vb=−5 volts.

[0042] The operation of the device, described previously, is thusestablished, in detail, as follows:

[0043] At a certain instant t1, the sensor 2 delivers an analogmeasurement signal Se, transformed firstly by the circuit 3 into adigitizable analog signal Ss, then converted, in the converter 4, into acorresponding digital value n1. The unit 5 (microprocessor) stores thevalue n1 corresponding to the instant t1, and it delivers, on its output7, the inversion signal Si. Receiving this signal Si, the inversioncircuit 8 orders the inversion of the supply of the sensor 2.

[0044] Thus, at a later instant t2, the sensor 2 delivers an invertedanalog signal Se, which is likewise matched by the circuit 3, thenconverted into a corresponding digital value n2. The unit 5(microprocessor) acquires this new value n2.

[0045] The unit 5 (microprocessor) sums the two numbers n1 and n2, andit compares the result of the summation, i.e. a number S=n1+n2, with theresolution R of the analog/digital converter 4.

[0046] If the system is operating correctly, the two values n1 and n2,which correspond respectively to the signals Se of the sensor 2 beforeand after inversion of its supply, should be complementary, statedotherwise their sum S is equal or approximately equal to the resolutionR of the converter 4. In this event, the unit 5 (microprocessor) enablesthe actuator 6 control signal Cm, corresponding to the control pre-setSc.

[0047] Conversely, if the system is operating incorrectly, the twovalues n1 and n2, corresponding respectively to the signals Se of thesensor 2 before and after inversion of its supply, are no longercomplementary, stated otherwise their sum S becomes significantlydifferent from the resolution R of the converter 4. In this event, theunit 5 (microprocessor) no longer enables the signal Cm, so that thecontrol of the actuator 6 is disabled. Simultaneously, themalfunctioning thus detected is taken into account, and signaled to theoperator, for example by display on a monitoring screen. The operatorthen has the possibility of noting the malfunctioning, and optionally ofgiving the go-ahead to a “degraded” mode of working.

[0048] The operation of the device is further illustrated by theflowchart of FIG. 2, as well as by the table below, in which areindicated the valves n1 and n2, respectively before and after inversionof the supply of the sensor, and their sum S, for the extreme values,the median value and any value of the control setting; this table isreferred to the normal state of the system, in which the sum S=n1+n2 isequal to the resolution R. Inversion Sensor of the Control signal Numbersupplies Number Sum (S) = setting (Se) (n1) (Se′ = −Se) (n2) n1 + n2Extreme Se = Va n1 = 0 Se = −Va = n2 = R n1 + n2 = value Vb R Median Se= 0 n1 = R/2 Se = 0 n2 = R/2 n1 + n2 = value R Extreme Se = Vb n1 = R Se= −Vb = n2 = 0 n1 + n2 = value Va R Any Va < n1 = ((Vb + Vb < −Se < n2 =((Vb − n1 + n2 = value Se < Vb Se)/(Vb − Va Se)/(Vb − R Va)) · R Va)) ·R

[0049] Observation of this table shows that the device is almost 100%reliable, since the only values which do not allow the detection of amalfunctioning by the process of the invention are situated in themiddle of the sensor's range, for which the value of the signal Se ofthis sensor (before or after inversion) is equal to zero. However, thisparticular position corresponds to a nonpreferential zone of use, whichis also a zone of nonrisk during use.

[0050] Moreover, the system is self-monitored since, if the securitydevice is itself defective, it does not order the inversion of thesupply of the sensor 2, so that the complementarity of the signals Se ofthis sensor, hence of the values n1 and n2, is no longer ensured. Thesystem then also goes faulty, automatically.

[0051] The process and the device which are the subject of the inventionare applicable to all types of safety using passive analog sensors,fitted to lifting apparatus and in particular tower cranes. They mayinvolve safety devices related to the use of the crane, when working:load limiters, torque limiters, motion (lifting, rotation, distributiontranslation) limiters. They may also involve more particular functionssuch as: monitoring of the kinematics for erecting the crane (forexample: simultaneous unfolding of the jib and of the mast), monitoringof stability (for example: tilt meter with jacks), monitoring of metalmembers (for example: monitoring of the voltage of the distributioncable), or other monitoring functions.

[0052] As goes without saying, and as emerges from the foregoing, theinvention is not limited solely to the embodiment of this device formaking secure the processing of safety signals which was describedabove, by way of example. On the contrary, it embraces all variantembodiments and variant applications thereof implementing the sameprocess. Thus, in particular, one would not be departing from the scopeof the invention by using any means carrying out the calculationoperations and the logic operations, namely the adding of the values n1and n2 and the comparing of their sum. By the same token, the inventionremains applicable to lifting apparatus of all sorts, its field ofapplication not being limited to tower cranes. Finally, although theinvention has been described with relevance to the processing of thesignal emanating from a single sensor, it will be clearly apparent tothe person skilled in the art that the same components, such as theconverter 4, the arithmetic and logic processing unit 5 and theinversion circuit 8, may also be common to several sensors (fitted tothe same lifting apparatus), and in this case may process the signalsdelivered by all these sensors.

1. Process for making secure the processing of safety signals, moreparticularly of a signal (Se) delivered by a sensor (2) of resistiveanalog type, supplied electrically with DC current, in a safety deviceon a lifting apparatus, the analog signal (Se) delivered by the sensor(2) being converted into a digital signal (n) in an analog/digitalconverter (4) of given resolution (R), the process being characterizedin that: at a first instant (t1), a digital signal (n1) corresponding tothe analog signal (Se) delivered by the sensor (2) is acquired andstored, then the supply voltages (Va, Vb) of the sensor (2) areinverted, after this inversion, at a later instant (t2), a new digitalsignal (n2) corresponding to the analog signal (Se′) delivered by thesensor (2) is acquired, the two digital signals (n1, n2) acquired aresummed, the sum (S) of these two digital signals is compared with theresolution (R) of the analog/digital converter (4), and if this sum (S)is equal or approximately equal to the resolution (R) of the converter(4), a control signal (Cm) for operating an actuator (6) of the liftingapparatus, corresponding to a control pre-set (Sc), is enabled, or ifsaid sum (S) is significantly different from the resolution (R) of theconverter (4), the control signal (Cm) is not enabled.
 2. Processaccording to claim 1, characterized in that the analog signal (Se),delivered by the sensor (2), is filtered and matched, so as to yield adigitizable analog signal (Ss) which is the signal to be converted,before and after inversion of the supply voltages of the sensor (2). 3.Process according to claim 1 or 2, characterized in that, in the casewhere the sum (S) of the two digital signals (n1, n2) is significantlydifferent from the resolution (R) of the analog/digital converter (4), asignaling is emitted to indicate the state of malfunctioning.
 4. Devicefor making secure the processing of safety signals, more particularly ofthe signal (Se) delivered by a sensor (2) of resistive analog type,supplied electrically with DC current, in a safety device on a liftingapparatus, the sensor (2) being linked to an analog/digital converter(4) of given resolution (R), which converts the analog signal (Se)delivered by the sensor (2) into a digital signal (n) transmitted to anarithmetic and logic processing unit (5) which also receives a controlpre-set (Sc), and which is able to deliver a control enable signal (Cm)for operating a motion actuator (6) for moving the lifting apparatus,the device being characterized in that it comprises, in combination:control means (7, 8) for inverting the supply voltages (Va, Vb) of thesensor (2), means (5) for acquiring the digital signals (n1, n2)corresponding to analog signals (Se, Se′) delivered by the sensor (2),respectively before and after inversion of its supply voltages, means(5) of summing the two digital signals (n1, n2) acquired, and ofcomparing the sum (S) of these two signals with the resolution (R) ofthe analog/digital converter (4), and means of enabling/disabling thecontrol (Cm) of the actuator (6), corresponding to the pre-set (Sc),according to the result of the comparison of the aforesaid sum (S) withthe resolution (R) of the converter (4).
 5. Device according to claim 4,characterized in that the sensor (2) is a potentiometer, the means ofcontrol of inversion (7, 8) carrying out the inversion of the supplyvoltages (Va, Vb) present at the terminals of the potentiometer. 6.Device according to claim 4 or 5, characterized in that an analogconditioning circuit (3), intended for filtering and matching the analogsignal (Se) delivered by the sensor (2), is interposed between thissensor (2) and the analog/digital converter (4).
 7. Device according toany one of claims 4 to 6, characterized in that the means of acquiringthe two digital signals (n1, n2), of summing these signals (n1, n2), ofcomparing the sum (S) of these signals with the resolution (R) of theanalog/digital converter (4), and of enabling/disabling the control (Cm)according to the result of the comparison, are incorporated into thearithmetic and logic processing unit (5), the latter possessing anoutput (7) linked to the means (8) of control of inversion of the supplyvoltages (Va, Vb) of the sensor (2), which means are embodied in theform of an inversion circuit (8).
 8. Device according to claim 7,characterized in that the arithmetic and logic processing unit (5),incorporating the means of acquiring the two digital signals (n1, n2),of summing these signals (n1, n2) and of comparing their sum (S) withthe resolution (R) of the converter (4), is embodied in the form of amicroprocessor.
 9. Device according to any one of claims 4 to 8,characterized in that it is applied to safety devices such as loadlimiters, torque limiters, motion limiters or speed limiters, or tomonitoring functions, provided on tower cranes, and using passive analogsensors (2).